1. Field of the Invention
The present invention relates generally to an automatic automotive transmission and more specifically to a control system for same which enables both select shock and shift shock attenuation.
2. Description of the Prior Art
In an automatic automotive transmission there is a general tendancy for so called "select shock" to be produced when a manual selector valve is moved from neutral (N) to the forward automatic drive range (D) due to the sudden coupling of the engine to the transmission (via a torque converter or the like). A known method of reducing this phenomenon is to couple the friction elements which produce a high speed gearing (preferably the highest) just prior those which produces first speed so as to reduce the effect of engine torque on the transmission.
One method of acheiving the above mentioned select shock attenuating gear selection is to detect engine idling and feed line pressure to the shift valves in place of the normal governor pressure under such circumstances, to induce same to assume their respective upshift positions. However, in the case of a three speed transmission wherein two clutches (e.g., a foward clutch and a high and reverse clutch) are provided, wherein first gear is produced when the forward clutch is engaged and third speed by engaging both of the clutches and wherein a one-way clutch is utilized so that first speed can be produced by engaging only the forward clutch; in order to reduce select shock, it is necessary to ensure that the high and reverse clutch is engaged slightly before the forward clutch. To achieve this it is possible to provide a flow restriction in the passage through which hydraulic fluid is fed to the forward clutch and no restriction or orifice in the fluid circuit through which the high and reverse clutch is pressurized. On the other hand, in order to prevent shift shock during a 2-3 shift, the pressure in the high and reverse clutch must be raised slowly enough to allow time for the release of the brake engaged to produce second gear. Viz., to reduce select shock it is necessary to rapidly pressurize the high and reverse clutch while, on the contrary, during a 2-3 shift the pressurization must be suitably delayed to avoid shift shock. Accordingly, a simple control arrangement via which both of these conflicting requirements can be readily obtained has been wanting.